This invention relates to a method and device for estimating the directions-of-arrival (DOAs) of the radio waves impining on the array antenna at a base station, where the directions of the incoming radio waves can be accurately estimated. More particularly, it relates to a method and device for estimating the DOAs of the radio waves with cyclostationarity without the need of the complicated eigendecomposition and can tracking the time-varying directions accurately and quickly.
Research and development on the applications of an adaptive array antenna for mobile communication is currently gathering attention, where multiple antenna elements are placed in different spatial positions with predetermined geometry. The estimation of the directions of the radio waves (hereafter the radio waves may be called “signals” from the signal processing point of view) impinging on the array antenna is one of the important fundamental technich for the adaptive array antenna. For the problem of direction estimation, subspace-based methods, which use the orthogonality between the signal subspace and noise subspace, are well known because of their estimation accuracy and computational complexity. But conventional subspace-based direction estimation methods require the eigenvalue decomposition (EVD) or singular value decomposition (SVD) of the array covariance matrix to obtain the signal (or noise) subspace.
In addition, in s of mobile communication systems, the signals from a user (mobile terminal) impinge on the array antenna of base station via a direct path and reflected path due to the various reflection from buildings, for example. Therefore the direction estimation of multiple waves in multipath propagation environment is very important problem in array processing.
Furthermore the directions of the impinging signals may change over time because of the movement of the user (signal source), so a direction tracking method is demanded to estimate the directions of the multiple waves in an online manner. Since conventional subspace-based methods require the eigendecomposition such as EVD or SVD, they are limited in some applications where the time-varying directions of the multiple waves should be estimated in an online way, because they require repeated EVD/SVD to update the signal/noise subspace with the acuqiusition of neww data and the deletion of the old data, which is computationally intensive and time-consuming. Therefore this invention proposes a new estimation method for estimating and tracking the directions of modulated communication signals having cyclostationairity without the needs of the eigendecomposition and spatial smoothing. And the present invention also proposes an online algorithm for tracking the time-varying directions of multiple signals in multipath environment.